This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Parasitic infections have a high energetic cost to the host that can reduce reproductive success. Females can reduce fitness losses by choosing mates to produce parasite resistant offspring. The Major Histocompatibility Complex (MHC) is responsible for immune activation against foreign pathogens and has been found to be a target of sexual selection. Presumably, coevolution with parasites has generated high levels of polymorphism in the MHC. Females can infer information about the MHC alleles through gene product metabolites that are detected as chemical signals or scents. The aim of this study is to determine the effects of sexual selection on the evolution of the MHC in the brown anole, Anolis sagrei. We propose that mate choice also accounts for the variability found in MHC genes. Very few lizards have been the focus of olfactory mate choice studies although it is well documented in fish, birds and mammals. The results of this study are necessary for a more complete comparative analysis of immune system evolution in concert with mate choice. A. sagrei will have MHC class I antigen binding regions amplified and sequenced to quantify polymorphisms and heterozygosity in individuals. In behavioral trials, female anoles will be presented with two males that either vary in MHC dissimilarity from the female or vary in level of heterozygosity at MHC loci. We expect that the naturally high levels of parasites in their environment should drive female preference for heterozygous males in order to produce offspring with high allelic diversity and thus better parasite resistance.